Ultracapacitors (Farad Capacitors) to Meet New Energy Storage Solution Options for High-Performance Power Applications
Supercapacitors offer high power and energy density, long life, and compact size, and when combined with other emerging battery technologies, can meet the needs of high-performance power applications. This paper provides an analysis of these new energy storage schemes and how they can be used.
Performance and reliability are required in every design these days, and for engineers, energy storage has always been the Achilles' heel in their designs. In the past, the solution for backup power was batteries, mainly lead-acid batteries. Now, engineers have more options to meet their backup power needs, including advanced battery technologies such as lithium-ion and nickel-metal hydride batteries, fuel cells, solar cells, and double-layer capacitors.
Lithium-ion, NiMH and other battery technologies have made great strides in providing reliable energy storage solutions. They have been used in many designs and solved many of the cost issues of the past, but design engineers still end up facing the same problems as when using lead-acid batteries, which is that all these technologies are based on chemical reactions and they have a limited lifespan And limited by temperature, and the demand for high current will also directly affect their service life. Therefore, these battery technologies still face some challenges in terms of durability and reliable application.
Fuel cells are a very attractive new battery technology that is gradually entering many applications, and there has been a lot of hype about them recently. The final application area for fuel cells is in automobiles, but in the interim, they have emerged in the backup power market. Key issues in using fuel cells as backup power sources as well as primary power sources are the start-up time and dynamic power response of these cells. Fuel cells, despite their excellent energy density, suffer from low dynamic power, so they require an enhanced technology for power assist and start-up.
Supercapacitors, or electrochemical double-layer capacitors (EDLCs), also appeared at the same time. Compared with electrolytic capacitors, supercapacitors have very high power density and substantial energy density. Over the past few years, these devices have been used in many fields such as consumer electronics, industrial and automotive.
Today, the best supercapacitors are ultra-high-power devices with power densities up to 20kW/kg, although the energy is still a fraction of that of batteries. Ultracapacitors are very compact in size (small ones are often the size of a postage stamp or smaller), but they can store much more energy than conventional capacitors and can discharge quickly or slowly. They have a very long service life and can be designed for the entire life cycle of the end product. When combined with the latest technology, supercapacitors, high-energy batteries and/or fuel cells can achieve high power characteristics and long operating life.
Although there are several ultracapacitor manufacturers around the world offering a variety of products, most double layer capacitors are basically constructed in a similar way. The structure of supercapacitors is very similar to that of electrolytic capacitors or batteries. The main difference is that the electrode materials used are different. In supercapacitors, the electrodes are based on carbon material technology, which provides a very large surface area. The large surface area and small charge separation enable supercapacitors to have high energy density. Most supercapacitors are rated in farads (F), usually between 1F and 5,000F.
Depending on the application, supercapacitors can replace batteries or act as smaller, economical batteries. Supercapacitors have a small equivalent series resistance (ESR) and can source and sink very large currents; they use a "mechanical" rather than a chemical charge carrier mechanism, resulting in long and predictable lifetimes, and Its performance has also changed less over time. These features can benefit applications such as regenerative braking and other products that require fast charging, such as toys and tools.
There are some applications where a battery/supercapacitor system is suitable and the design can be optimized to avoid the battery being too bulky for the energy demands. Examples of these applications include automotive applications (eg, hybrid vehicles) and consumer electronics (eg, digital cameras), where inexpensive alkaline batteries are used in conjunction with supercapacitors (while
Another fuel cell technology is the proton exchange membrane (PEM), which is a high-efficiency energy conversion device with a continuous operating time comparable to that of a hydrogen fuel cell. It meets green environmental protection requirements and can provide reliable backup power for many applications. Several properties of supercapacitors and PEM fuel cell systems make them ideal for use together as complementary devices. They are all low-voltage, high-current devices. Supercapacitors have the characteristics of small ESR and large charge storage capacity, which can quickly supply large currents with small voltage changes, and can produce a brief buffer response to peak power demands. This allows the fuel cell to maintain its static operating point without reducing efficiency.
In all backup fuel cell applications, the backup power supply needs to provide power immediately after the main power supply is lost. Because a fuel cell typically requires a start-up time of 10 to 60 seconds from start-up to full power operation, it requires an energy buffer. A battery or supercapacitor can act as this energy buffer. Since the required buffer energy is small and reliability must be guaranteed, supercapacitors are a better choice for this application. Today, more and more fuel cell companies are considering ultracapacitors as an integral part of the overall backup power package.
To meet this demand, global supercapacitor producers provide many batteries and modules for the backup power market. These cells and modules can be placed in parallel/serial to meet different capacity and voltage requirements. As more supercapacitor products become available and more products become available, design engineers can use supercapacitors just like any other passive device.
Ultracapacitors have come a long way in becoming a standard device for backup power. About a decade ago, supercapacitors were just samples in the lab, only sold in small numbers each year, priced between $1 and $2 per farad of capacity. Today, these mass-produced devices are considered standard and cost as little as 0.01 to 0.02 cents per farad of capacity. As the production of supercapacitors increases and prices fall, many design engineers are using supercapacitors as standard energy storage devices to meet the high power and reliability requirements of backup power supplies.